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EPA information - worth anything?

I've new to this website. My wife and I are doing research to determine which Hybrid car we will purchase. We love the Lexus GS450 (even though it's gas mileage isn't that great), but we are getting conflicting information on emission information. The car review on this website states "Fewer still boast, as this Lexus does, of being rated a Super Ultra-Low Emissions Vehicle (SULEV) in California, which certifies a car's emissions are 90 percent cleaner than the average new car offered in California in 2004." The review of the Prius states that it's SULEV is 89%, slight worse. The EPA website has a "Green Vehicle Guide" (http://www.epa.gov/greenvehicles) which displays separate scores for pollution and greenhouse gas emissions. The pollution scores are based on the amount of nitrous oxide, carbon monoxide, etc emitted by the vehicle. The greenhouse gas scores is based strictly on carbon dioxide emissions. The detailed description goes on to state that the amount of carbon dioxide is determined by fuel efficiency and fuel type. Based on that the Lexus GS450 gets only a score of 7 of 10, where the Prius is 10 of 10. Also, the pollution score for Lexus is 9 of 10, where the Prius is 9.5 of 10.

So ... how can the Lexus be slightly cleaner (SULEV rating) than the Prius if this EPA information is accurate?

Good Question

I made an effort to find out the answer to your good question. Everything points to the Prius review used the number 89% instead of 90%. I expect that this is the cause since the criteria for the CARB SULEV rating is to be better than 90% of the car average. Everything else points to the Prius being the lower emissions vehicle. The Prius has the following technologies you might not have in the Lexus, so these might be good leads to followup.
1) There is a insulated water tank to preserve the engine heat so that the engine is rapidly returned to the operating temperature for absolute minimum pollution on the next start.
2) There is a fuel bladder inside the fuel tank so that fumes cannot form and then escape.
3) The engine operates on a "Atkinson" cycle. The "Otto" cycle is probably what the Lexus uses. (Use Wikipedia for more info.)

Since all pollution is measured on how efficiently a gallon of gas is used, the 55 mpg Prius vs. 28 mpg Lexus may be a factor for you. [But my brother points out he travels 3 miles a day (SUV) vs. my 40 miles (Prius), so you can easily generate less pollution than me in a Lexus.]

Now a thanks to you for making an effort to base your buying decision with some research on car emissions. I'm a fan of both the Prius and Free Choice.